Testing the User's Response

In this program, no special number is suitable as a sentinel because any number is potential data. Because of this, there must be a prompt that asks if the user wants to continue, and another prompt that asks for data.

Here is an outline of the program:

class evalPoly
{
  public static void main (String[] args ) throws IOException
  {

    double x;                      // a value to use with the polynomial
    String response = "y";         // "y" or "n"

    while ( response.equals("y") )    
    {
       // Get a value for x.

       // Evaluate the polynomial.

       // Print out the result.

       // Ask the user if the program should continue.
       // The user's answer is "response".
      
    }

  }
}

It is often useful to work on one aspect of a program at a time. Let us first look at the "prompting and looping" aspect and temporarily ignore the polynomial evaluation aspect.

The condition part of the while statement, response.equals("y") evaluates to true or false. Here is how this happens:

• response is a reference to a String object.
• A String object has both data and methods (as do all objects).
• The data part of response will be the characters that the user types.
• There are several methods for a String object. The equals( String ) method tests if two Strings contain the same characters.
• response.equals("y") tests if the String response is equal to the String "y".
• The result of the test is true or false.

In other words, the condition response.equals("y") asks: did the user type a "y"?